In optical technology, recently, active research for developing high-precision sensors capable of measuring biomolecules, nanoparticles, deuterium ratios, etc. has been studied by means of an ultra-high quality factor resonator. For such applications, a circular resonator has been used, where a whispering gallery mode is formed inside the circular resonator by introducing an external light source into the circular resonator. Then, when a biomolecule or a nanoparticle is adhered to the surface of the circular resonator, the wavelength is shifted in a resonance mode. Development has been conducted on techniques for measuring such a shift to detect a biomolecule or a nanoparticle. In this case, a quality factor (i.e., Q factor) needs to be extremely high in order to measure a very small variation of the wavelength formed by the adhesion of the biomolecule or nanoparticle. Since such an ultra-high quality factor resonator is implemented by only a circular resonator, development of sensors has been focused on a circular resonator.
However, since a circular resonator emits light in all directions and needs to couple with an external light source, an optical fiber has to be closely coupled with the resonator so that the emitted light can be delivered through the optical fiber. However, in this coupling, there is a drawback, that is, when the position of the optical fiber is slightly changed, the quality factor of the resonator decreases or the optical fiber does not well couple with the resonator. Also, in such a shape, measurement is not properly achieved when the optical fiber is perturbed even by small external vibration. Therefore, a sensor using a circular resonator has a great problem in commercialization due to these problems.
A resonator capable of solving the problems is a unidirectionally emitting microdisk laser. As unidirectionally emitting microdisk lasers, a spiral shape, a rounded triangular shape, a Limagon shape, an ellipse with a notch shape, a half-circular and half-elliptic shape have been proposed up to now.
However, the unidirectionally emitting microdisk lasers that have been developed up to now are highly unidirectional but their quality factors are low, and thus the unidirectionally emitting microdisk lasers that have been developed up to now have still many challenges to be overcome for commercialization. A circular resonator has a quality factor of up to 109, but deformed resonators capable of unidirectional emission has a quality factor of less than 106. When an ultra-high quality factor microdisk resonator that emits unidirectional light is achieved, the ultra-high quality factor microdisk resonator can unidirectionally emit light while maintaining a high quality factor. Accordingly, it is possible to develop the ultra-high quality factor microdisk resonator as an ideal sensor.